1999 Gs300 Engine Rattle/knock/noise

[SinGarage]

Good evening all. I would like to come to the Gurus of the Lexus forum for help about my GS300.

There is a noise in the engine that is driving me nuts. I have made multiple searches in this forum and Google and cannot seem to find the solution. The noise is intermittent at idle but almost 90% there when the A/C is on. This would typically lead me to the AC compressor (clutch, bearing, etc.) but it also does it when I let go of the gas (with the AC off). I had made some youtube videos of it today so you can see and hear what I am talking about. I also thought it could be the belt tensioner as it would also be related. I have changed it with a new one and it still does not change the problem. I am really hoping it is not a rod knock but I really don't think it is as it does it after I let go of the gas. I have not made any tests on the rod knock yet as it is really late here and my neighbors wouldn't be too happy.

This is with the AC on. You can clearly hear the rattle/noise.

This is with the AC off but revving it. You could hear the same sound right when I let go of the throttle.

Any help would be greatly appreciated.

Thanks,

SinGarage

[intakerGS]

Apparently, the rattle occurs when you put 'load' on the engine. It strongly sounds like a bad rod bearing, although my desktop speakers are rather limited.

Do you experience unusual oil consumption, perhaps engine running on low oil in the past?

Is it possible for you to isolate the noise to an area? You need to exclude loose parts, like an exhaust shield for example. Best would be a mechanics stethoscope, if not at hand, place the tip of a large scewdriver on a possible source and listen to the other end. Start with the rod area.

[williamJ]

I think I have the exact same noise.

It started as a sort of squeal only when cold and much more so with the ac on. I removed the serpentine belt (so no ac, water pump, alternator or p/steering pump) and started it cold - noise still there! I changed the timing belt and tensioner but it wasn't either tensioner. Noise gradually got worse and became a very definite rattle or knock and it seemed to be coming from the middle of the engine on the left side. I saw posts about the VVTi going bad but I cannot find anything wrong there. Without a new oil control solenoid (voltage varies between 1 and 5 volts on a live test run) and VVTi gear to substitute I can't be 100% sure though. It does sound very like a detonation rattle but the knock sensor seems to be fine and the timing does seem to be wrong using a strobe. It's all very weird.

I agree that rod knock seems to be a possibility but it does not follow the pattern. If its a rod knock it is intermittently one or several of them! I checked the oil pressure which seems to be within spec.

I find the noise is worse when the engine is warm and much worse when the ac or fans are running. It is improved by engaging drive. That bit is really weird - how on earth would that change a rod knock? It does not appear at all when cruising low (20) or medium (70mph) speed. When I lift off the gas at 20mph it rattles briefly though.

My oil consumtion is fine the valve clearances are fine, never been run low on oil or overheated.

A mechanic who heard it has suggested that it could be to do with the transmission - he thinks maybe drive plate.

Does anyone recognise any of this and maybe shed some light?

[williamJ]

After much research it seems this is highly likely to be a broken torque converter flex plate / drive plate, which joins the crank to the torque converter. I don't want to remove the box myself so I am having it looked at on Tuesday by a transmission shop. They say the plates are usually broken when they make a rattle but occasionally it is just loose bolts. The plate will cost $275 from Lexus if it is needed. A new torque converter costs $1600 ouch - but they tell me they are usually fine. Hope the crank isn't damaged.....

[intakerGS]

TX for sharing this. Always good to see a solution. Good luck!

[williamJ]

TX for sharing this. Always good to see a solution. Good luck!

Well I took it to a local transmission shop that had a recommendation - I really didn't like the idea of trying to get the box out without a lift and a workshop. They replaced the flex plate / drive plate which was cracked 8/10ths of the way around the outside of the crankshaft bolts. Bolts had not come loose. Torque converter was fine. It was very noisy on the day I drove it to the shop but it hung together just long enough. The shop charged $500 labour. It is once again a pleasure to drive.

While I was checking the rest of the engine over I took out the spark plugs (not a 5 minute job!!) The plugs had done 90,000 miles. They were all fine. Clearances slightly larger than spec but in very good condition. I put them back - I needed the $90 to put to the gearbox work

[FERNDOGGS3]

Hello

I own a 2000 lexus GS300 with 240k miles i also think i have a problem with my fly wheel but my car only makes a noise, not like yours, mine is a thump right before i come to a complete stop. I got under and searched only thing i noticed is my fly wheel is rubbing on something but it didn't looked cracked.

Did yours make that noise to right before you came to a stop?

Thanks

[Fanuel]

I have a lexus GS300. It drives very well buy 2 weeks ago it started giving a rattle noise which sounds like its coming from bottom of engine. The car moves very well but when in low raves you hear the noise. My mechanic is not sure but thinks its a knock. the temperature of the car never went high.